1. Field of the Invention
The present invention relates to an elbow which is suitable for connecting pipes, and a method for manufacturing such corrugated resin elbow. Although not elated directly to the size of the diameter of a pipe, this invention is mainly in the bent pipe portion of a large-sized pipe having an inside diameter of the order of 1,000 mm-2,000 mm.
2. Description of the Related Art
An conventional elbow of this type and a method for manufacturing the same is shown in FIGS. 10 to 19. A synthetic resin pipe P of a desired length includes a pipe wall 1 having a spirally corrugated shape. The synthetic resin pipe member P is cut in an inclined direction along a cutting line C having a desired inclination angle as shown in FIG. 11. Then, as shown in FIG. 12, the thus cut and divided pipes are turned in the circumferential direction thereof to change the angles of the cut surfaces to thereby change the relative angle of the cut surfaces of the cut and divided pipes. Next, the cut end faces are butted against each other and are thereby connected with each other in a watertight manner (for example, see Japanese Patent Publication No. Hei. 4-44157, especially, FIG. 1).
Referring here in more particular to the accompanying drawings, to manufacture an elbow E having an angle of 45.degree. shown in FIG. 14, the middle portion of the spirally corrugated synthetic resin pipe member P is used as a pipe blank. As shown in FIG. 10, the synthetic resin pipe member P is cut along the cutting line C inclined at an angle of 22.5.degree. with respect to a line intersecting at right angles to the longitudinal direction of the resin pipe member P to thereby divide the pipe member P into two pipe members p and p'. One pipe member p of the thus cut and divided two pipe members is rotated by 180.degree. in the peripheral direction thereof to change the angle of the cut surface thereof to thereby change the relative angles of the cut surfaces of the cut and divided two pipe members p and p' (See FIG. 11 and 12). The cut end faces f and f of the two pipe members p and p' are butted against each other (See FIG. 13), then both sides of the butted surface F are connected together at a plurality of positions by wire members w such as wires. Next, sheet-shaped connecting material g, which is formed of the material that is similar to the pipe material and can be fused with the pipe material, is thermally fused and is thus applied repeatedly onto the outer periphery of the butted surface F to thereby close or seal spaces existing in the spirally corrugated cut surface of the butted surface F. The inner surface side portions of the pipe members p and p' are similarly sealed to thereby connect together the two pipe members p and p' in a watertight manner, thereby manufacturing the elbow E.
Now, FIGS. 15 to 19 respectively show the time sequencing steps of a method for manufacturing an elbow having an angle of 90.degree. shown in FIG. 19. In the present elbow manufacturing method, as shown in FIG. 15, the two sides of the middle portion of a synthetic resin pipe member P to be used as a blank are cut along two cutting lines C and C respectively inclined at angles of 22.5.degree. and -22.5.degree. with respect to a line intersecting at right angles to the longitudinal direction of the pipe member P to thereby cut the pipe P into two side pipe members p, p and an intermediate pipe member p'. Then, the intermediate pipe member p' is rotated by 180.degree. in the circumferential direction thereof to thereby change the angles of the cut surfaces f' and f' thereof (See FIGS. 16 and 17). Next, the cut surfaces f and f of the two side pipe members p and p are respectively butted against the cut surfaces f' and f' of the intermediate pipe member p' (See FIG. 18). Next, the thus butted surfaces F and F are connected in a watertight manner by similar means to the above-mentioned case, thereby manufacturing the elbow E. In addition, instead of the above-mentioned sheet-shaped connecting material, a glass fiber sheet is repeatedly applied using fused resin.
As described above, since, to manufacture this type of conventional elbow E, there is employed the means in which the spirally corrugated pipe is cut at a desired angle, the angles of the thus cut surfaces are changed and the present cut surfaces are butted against each other, and the butted surfaces are connected together again in a watertight manner. However, it takes labor, time and skill to seal positively the large spaces produced in the spirally corrugated portions of the butted surfaces to thereby connect the divided pipe members in a watertight manner. Furthermore, although the elbow E is manufactured by spending such time and labor, if the elbow E is vibrated or treated improperly during transportation, or if biased loads such as uneven loads are applied to the elbow E after it is buried in the earth, then water is easy to leak in the elbow E.